Mixing software based compression requests with hardware accelerated requests

ABSTRACT

A computer program product for data compression is provided. The computer program product includes a computer readable storage medium having program instructions embodied therewith. The program instructions are readable and executable by a processing circuit to cause the processing circuit to execute software compression for first requests for data compression that have respective sizes below a predefined threshold, forward second requests for data compression having respective sizes above the predefined threshold to a hardware accelerator and maintain a persistence of a compression dictionary used for executing the second requests across executions of the first and second requests.

BACKGROUND

The present invention relates to accelerated compression requests and,more specifically, a process for mixing software based compressionrequests with hardware accelerated requests for a single file.

There is an industry wide direction to introduce specialized hardwareaccelerators for central processing unit (CPU) intensive functions, someof which include data compression operations. Devices of this nature aremore valuable if they can be transparently integrated into existingworkloads and applications.

In order to provide for transparent integration of hardwareaccelerators, some issues need to be addressed. First is that thehardware accelerators will have different latency and speed attributesfor compression than performances of compression operations in puresoftware. One of these speed attributes could be the overhead incommunicating with the device. That is, due to this potential overheadthere will be a minimum size of data which will need to be provided inorder to amortize that overhead. Ideally any software package wouldprovide large amounts of input per request. There are conditionshowever, due to protocol or data format standards, where large requestswill be intermixed with very small requests that typically carrymetadata information about the payload. In this environment, use ofhardware accelerators for both large and small requests will impact theoverall performance of a compression operation of a single file.

The zlib open source library provides the standard programming interfacefor using the DEFLATE compression file format. The IBM zEnterprise DataCompression (zEDC) support extended the zlib library to use either itsexisting software interfaces or the new zEDC hardware to performcompression. Today, the determination to use either the software orhardware compression is made on a per-file basis based on the size ofthe first request for that file. This method has two shortfalls. Thefirst of these shortfalls is that the request may be very small but maybe followed by many large requests. The second shortfall is that thefirst request may be very large and followed by or intermixed with manyvery small requests. In both of these cases the existing support cannotuse the hardware acceleration to achieve the best possible throughputfor compressing the file.

SUMMARY

According to an embodiment of the present invention, a computer programproduct for data compression is provided. The computer program productincludes a computer readable storage medium having program instructionsembodied therewith. The program instructions are readable and executableby a processing circuit to cause the processing circuit to executesoftware compression for first requests for data compression that haverespective sizes below a predefined threshold, forward second requestsfor data compression having respective sizes above the predefinedthreshold to a hardware accelerator and maintain a persistence of acompression dictionary used for executing the second requests acrossexecutions of the first and second requests.

According to another embodiment of the present invention, a computersystem for data compression is provided. The computer system includes acomputer readable storage medium having instructions stored thereon thatare executable by a processing circuit to cause the processing circuitto execute software compression for first requests for data compressionthat have respective sizes below a predefined threshold, forward secondrequests for data compression having respective sizes above thepredefined threshold to a hardware accelerator and maintain apersistence of a compression dictionary used for executing the secondrequests across executions of the first and second requests.

According to yet another embodiment of the present invention, acomputer-implemented method for data compression is provided andincludes executing software compression for first requests for datacompression that have respective sizes below a predefined threshold,forwarding second requests for data compression having respective sizesabove the predefined threshold to a hardware accelerator and maintaininga persistence of a compression dictionary used for executing the secondrequests across executions of the first and second requests.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as the invention is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The forgoing and other features, and advantages ofthe invention are apparent from the following detailed description takenin conjunction with the accompanying drawings in which:

FIG. 1 is a schematic illustration of a computing system;

FIG. 2 is a schematic diagram of an interior of a computing device;

FIG. 3 is a schematic drawing of a computer program product;

FIG. 4 is a schematic drawing of functionalities of the computer programproduct of FIG. 3;

FIG. 5 is a schematic illustration of program instruction components ofthe computer program product of FIG. 3.

FIG. 6 is a flow diagram illustrating an operation of the computerprogram product of FIG. 3;

FIG. 7 is a flow diagram illustrating a deployment process of thecomputer pro gram pro duct; and

FIG. 8 is a flow diagram illustrating a computer-implemented method ofdata compression.

DETAILED DESCRIPTION

As will be described below, a computer program product, a computingsystem and a computer-implemented method are provided that mix the useof hardware and software compression capabilities for a single filerequest while maintaining an opacity of the software compressionfunction (e.g., the existing zlib library) with respect to the hardwareapproach. This allows for a robust implementation as well as the abilityto extend the support to other libraries.

With reference to FIG. 1, a computing system 10 is provided and may beconfigured for example as an enterprise computing system or as apersonal computing system. In either case, the first computing system 10includes first, second and third computing devices 11, 12 and 13 andservers 15 which are configured to be networked together forcommunication purposes. Each of the first, second and third computingdevices 11, 12 and 13 and the servers 15 may include among otherfeatures a processing circuit 20, a display 30, user input devices 40and a networking unit as well as a computer program product 100 for datacompression. The processing circuit 20 may be provided as amicro-processor, a central processing unit (CPU) or any other suitableprocessing device. The display 30 may be provided as a monitor and isconfigured to display data and information as well as a graphical userinterface to an administrator or user. The user input devices 40 may beprovided as a mouse and a keyboard combination and are configured toallow the administrator or user to input commands to the processingcircuit 20. The networking unit may be provided as an Ethernet or othersuitable networking device by which the first, second and thirdcomputing devices 11, 12 and 13 and servers 15 are communicative.

With reference to FIG. 2, a structure and an interior of one of thecomputing devices 11, 12 and 13 and the servers 15 are illustrated. Forthe purposes of clarity and brevity, the structure and the interior willbe that of the computing device 11 although it is to be understood thatany of the computing devices 11, 12 and 13 and the servers 15 could havebeen chosen for discussion. As shown in FIG. 2, the computing device 11includes a housing 110 having a bottom portion, sidewalls and a lidformed to define an interior 111. The computing device 11 furtherincludes a motherboard 112, a hard disk drive (HDD) 113, a fan 114 forgenerating a cooling air flow in the interior 111 and a power supplyunit 115 for providing power to the computing device 11. A centralprocessing unit (CPU) 116, a memory unit 117 and at least one or moreremovable cards 118 are operably installed on the motherboard.

It is to be understood that the at least one or more removable card 118may be installed/soldered onto a same or a different motherboard as theCPU 118.

The at least one or more removable cards 118 may include, for example, ahardware accelerator card 119, a graphics processing unit (GPU) and/or afield programmable gate array (FPGA). However, for purposes of clarityand brevity it is to be understood that the following descriptionrelates to the case where the at least one more removable cards 118 isthe hardware accelerator card 119.

The hardware accelerator card 119 serves as computer hardware thatperforms some functions (e.g., data compression) faster than softwarerunning on the CPU 116. In any case, the hardware accelerator card 119is configured to handle certain types of data compression requests and,in particular, may be configured and disposed to handle relatively largedata compression requests and to do so at a relatively high level ofefficiency. That is, a throughput of the hardware accelerator card 119is or may be substantially higher than that of the CPU 116 for a similardata compression execution. This efficiency is important to note becausethere are time and processing costs associated with sending datacompression requests to the hardware accelerator card 119 from the CPU116. These time and processing costs are amortized over the timerequired to execute the relatively large data compression requests.

With reference to FIGS. 3 and 4, the computer program product 100includes a computer readable storage medium 1001 and may be installed inthe memory unit 117 of the computing device 11 as firmware or as lowerlevel executable program instructions. As such and, as shown in FIG. 4,the computer program product 100 defines a high-level software librarywrapper 1002, a data compression analysis unit 1003, an acceleratedcompression unit 1004, an accelerated compression dictionary 1005 and asoftware compression unit 1006. The high-level software library wrapper1002 manages data compression executions for the computing device 11 andis coupled to the accelerated compression unit 1004, the acceleratedcompression dictionary 1005 and the software compression unit 1006. Theaccelerated compression unit 1004 may be embodied in the hardwareaccelerator card 119 and the software compression unit 1006 may beembodied in the CPU 116. The data compression analysis unit 1003 managesdata executions for the computing device 11 in accordance with thedescription provided below. The data compression analysis unit 1003 maybe embodied in the CPU 116 and the accelerated compression dictionary1005 may be embodied in the CPU 116, the hardware accelerator card 119or another similar computing element.

The accelerated compression dictionary 1005 may be provided as adictionary coder or as a substitution coder. In any case, theaccelerated compression dictionary 1005 is formed of lossless datacompression algorithms that operate by searching for matches betweendata to be compressed and a set of strings contained in a compressiondictionary data structure 120 that is maintained by the acceleratedcompression dictionary 1005. When the accelerated compression dictionary1005 finds a match, it substitutes a reference to the string's positionin the data and thus avoids the need to copy and transfer the entiretyof the matching data. In accordance with embodiments, the compressiondictionary data structure 120 may be 32 KB from start to finish.

During operations of the accelerated compression dictionary 1005, thecompression dictionary data structure 120 is initially empty orreset/zeroed. Over time, as more and more matching data strings areencountered, the compression dictionary data structure 120 is filleduntil it reaches maximum capacity. At this point, any further datastrings to be added to the compression dictionary data structure 120 areadded onto its end with the corresponding deletion of older data stringsat the start.

With reference to FIG. 5, the computer program product 100 includesfirst program instructions 121, second program instructions 122 andthird program instructions 123. The first program instructions 121 causethe CPU 116 operate at least partially as the software compression unit1006 to execute software compression for first data compression requeststhat have respective sizes below a predefined threshold. The secondprogram instructions 122 cause the CPU 116 to forward second datacompression requests having respective sizes above the predefinedthreshold to the hardware accelerator card 119 where those second datacompression requests can be executed more efficiently than they could beexecuted by the software compression unit 1006. The third programinstructions 123 cause the CPU 116 to maintain a persistence of thecompression dictionary data structure 120 for use in the executions ofthe second data compression requests across the executions of both thefirst and second data compression requests.

In accordance with embodiments, the predefined threshold may be manuallyor automatically set. In the latter case, the predefined threshold isautomatically set by taking into account at least one or both ofhistorical compression request data and historical performance data ofthe hardware accelerator card 119. In general, the historicalcompression request data and historical performance data of the hardwareaccelerator card 119 may be considered in order to maintain anefficiency and throughput of the hardware accelerator card 119.

The first-third program instructions 121-123 are independent of theprogram library being used. Thus, any programming library that supportsa hardware accelerator card and has a complementary softwareimplementation can leverage the first-third program instructions121-123. Moreover, the third program instructions 123 provide value asthe compression dictionary data structure 120 of the acceleratedcompression dictionary 1005 is maintained even if a small request isprocessed with the software compression unit 1006 without the need forsoftware to manipulate the accelerated compression dictionary 1005 in apotentially costly and error prone manner. In addition, the maintenanceof the compression dictionary data structure 120 of the acceleratedcompression dictionary 1005 allows for better compression ratios fornext large data compression requests.

In accordance with embodiments, the executions of the first datacompression requests by the software compression unit 1006 may includeat least one of compression performance with a limited look-back contextto thereby reduce a memory footprint and a repackaging of request datainto a copy block. In the latter case, the software compression unit1006 does not compress data subject to the first data compressionrequest but instead repackages the data into the copy block. Here, thedata may be in a predefined format (e.g., a DEFLATE format) butcontinues to be in its raw non-compressed form. This repackaged data maybe padded or not padded onto a byte boundary. In the latter case,repackaged data not padded onto a byte boundary needs to be tracked and,in some cases, manipulated by the software compression unit 1006.

In accordance with further embodiments, the executions of the first datacompression requests by the software compression unit 1006 will notnormally make use of or rely upon the compression dictionary datastructure 120 of the accelerated compression dictionary 1005. However,in an event that a large set of the first data compression requests aredetermined to be processed, in the state of being processed or about tobe processed, a full compression context could be setup so thatlookbacks to the compression dictionary data structure 120 can beperformed and such that compression ratio is not negatively impacted.

In accordance with embodiments, the maintenance of the persistence ofthe compression dictionary data structure 120 by the third programinstructions 123 relates to various types of manipulations of thecompression dictionary data structure 120 for future second datacompression requests that are to be handled by the hardware acceleratorcard 119. In the simple case, the compression dictionary data structure120 can be zeroed so it is effectively reset every time one of the firstrequests is processed by the software compression unit 1006. As analternative to performing a dictionary reset, however, in an event thereis a partially or fully populated compression dictionary data structure120, the compression dictionary data structure 120 may be manipulatedthrough an adjustment of the starting location thereof. A size of suchadjustment may be equal or substantially similar to the size of thefirst request(s) handled by the software compression unit 1006.

Once the adjustment of the compression dictionary data structure 120 iscompleted, the size of the adjustment is provided to the hardwareaccelerator card 119. In this way, every back reference to thecompression dictionary data structure 120 by the hardware acceleratorcard 119 can be altered as an offset. That is, as back references arefound, the offset will be added to the distance of that back referenceto obtain the actual location in the original file being compressed. Theprocess can be repeated if there are multiple first requests executed bythe software compression unit 1006 consecutively by keeping ormaintaining a running sum of the sizes of the first requests and usingthat running sum as the offset value.

The processes laid out above will now be further described withreference to the flow diagram of FIG. 6. As shown in FIG. 6, a datacompression request is received by the data compression analysis unit1003 at block 601 and, at block 602, the data compression analysis unit1003 determines whether the data compression request is a first (i.e.,small) or second (i.e., large) data compression request. In an event thedata compression request is a first data compression request, the firstdata compression request is forwarded to the software compression unit1006 where an offset update (e.g., a size of an offset associated withthe data compression request) is calculated at block 603 and softwarecompression is executed at block 604 (by, e.g., compression with alimited look-back context or a repackaging of request data into a copyblock with padding/tracking and manipulation) and from which the offsetupdate information is sent to the hardware accelerator card 119 at block605 in order to inform the hardware accelerator card 119 of the offsetupdate.

On the other hand, in an event the data compression request is a seconddata compression request, the second data compression request isforwarded to the hardware accelerator card 119. Within the hardwareaccelerator card 119, it is determined whether execution of the seconddata compression request requires an offset or not at block 606. In anevent that no offset is needed, execution of the second data compressionrequest by the hardware accelerator card 119 commences at block 607.However, in an event that an offset is needed, execution of the seconddata compression request by the hardware accelerator card 119 proceedsby instituting the offset at block 608 and then executing the seconddata compression request by the hardware accelerator card 119 at block609.

After the second data compression request using the padded compressiondictionary data structure 120 is complete, the compression dictionarydata structure 120 is re-primed for a next second data compressionrequest. In the re-priming, it is to be understood that, if the previoussecond data compression request was 32 KB or larger, the padding spacewould naturally have been pushed out of the compression dictionary datastructure 120 whereas, if the previous second data compression requestwas smaller than 32 KB, the compression dictionary data structure 120can be truncated after current padding space and the next compressiondictionary data structure 120 would be the size of the last request.

With this understood, the hardware accelerator card 119 may beconfigured to maintain the padding space in the compression dictionarydata structure 120 and the software compression unit 1006 can pass backa list defined dictionary describing the areas, for example as a bitarray, where each bit represented the validity of one or more bytes.This would allow for ‘holes’ to be present in the compression dictionarydata structure 120.

While it is understood that the first-third program instructions 121-123may be deployed by manual loading thereof directly into a client, serverand/or proxy computer by way of a loadable storage medium, such as a CD,DVD, etc., or by being manually inserted into the computing device 11,the first-third program instructions 121-123 may also be automaticallyor semi-automatically deployed by being downloaded into client computersthat will then execute the first-third program instructions 121-123.Alternatively, the first-third program instructions 121-123 may be sentdirectly to a client system via e-mail for detachment or loading into adirectory or directly into a client computer hard drive. When there areproxy servers, loading processes will select proxy server codes,determine on which computers to place the proxy servers' codes, transmitthe proxy server codes and then install the proxy server codes on proxycomputers. The first-third program instructions 121-123 will then betransmitted to the proxy server and subsequently stored thereon.

In accordance with embodiments and, with reference to FIG. 7, adeployment process of the computer program product described above isprovided. The process begins at block 300 and at block 101 with adetermination of whether the first-third program instructions 121-123will reside on servers when executed. If so, then the servers that areidentified at block 209. The first-third program instructions 121-123are then transferred directly to the servers' storage via FTP or someother protocol or by copying though the use of a shared file system atblock 210 such that the first-third program instructions 121-123 areinstalled on the servers at block 211.

Next, a determination is made on whether the first-third programinstructions 121-123 are to be deployed by having users access to thefirst-third program instructions 121-123 on servers at block 102. If so,the server addresses that will store the first-third programinstructions 121-123 are identified at block 103 and a determination ismade if a proxy server is to be built at block 200 for storage. A proxyserver is a server that sits between a client application, such as a Webbrowser, and a real server and operates by intercepting all requests tothe real server to see if it can fulfill the requests itself. If not,the proxy server forwards the request to the real server. The twoprimary benefits of a proxy server are to improve performance and tofilter requests.

If a proxy server is required, then the proxy server is installed atblock 201 and the first-third program instructions 121-123 are sent tothe servers via a protocol, such as FTP, or by being copied directlyfrom the source files to the server files via file sharing at block 202.Another embodiment involves sending a transaction to the (one or more)servers that contained the process software, and have the server processthe transaction and then receive and copy the process software to theserver's file system. Once the process software is stored at theservers, the users may then access the first-third program instructions121-123 on the servers and copy to the same to their respective clientcomputer file systems at block 203. Alternatively, the servers mayautomatically copy the first-third program instructions 121-123 to eachclient and then run an installation program for the first-third programinstructions 121-123 on each client computer whereby the user executesthe program that installs the first-third program instructions 121-123on his client computer at block 212 and then exits the process at block108.

At block 104, a determination is made as to whether the first-thirdprogram instructions 121-123 are to be deployed by being sent to usersvia e-mail. If a result of the determination is affirmative, the set ofusers are identified together with the addresses of the user clientcomputers at block 105 and first-third program instructions 121-123 aresent via e-mail to each of the users' client computers, as shown atblock 204. The users then receive the e-mail at block 205 and detach thefirst-third program instructions 121-123 from the e-mail to a directoryon their client computers at block 206. The user executes the programthat installs the first-third program instructions 121-123 on his clientcomputer at block 212 and then exits the process at block 108.

Lastly, a determination is made on whether the first-third programinstructions 121-123 will be sent directly to user directories on theirclient computers at block 106. If so, the user directories areidentified at block 107 and the process software is transferred directlyto the user's client computer directories at block 207. This can be donein several ways such as, but not limited to, sharing the file systemdirectories and then copying from the sender's file system to therecipient user's file system or, alternatively, using a transferprotocol such as File Transfer Protocol (FTP). The users access thedirectories on their client file systems in preparation for installingthe first-third program instructions 121-123 at block 208, execute theprogram that installs the first-third program instructions 121-123 atblock 212 and then exit the process at block 108.

With reference to FIG. 8, a computer-implemented method for datacompression is provided and includes executing software compression forfirst requests for data compression that have respective sizes below apredefined threshold at block 801, forwarding second requests for datacompression having respective sizes above the predefined threshold to ahardware accelerator at block 802 and maintaining a persistence of acompression dictionary used for executing the second requests acrossexecutions of the first and second requests at block 803.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

The present invention may be a system, a method, and/or a computerprogram product at any possible technical detail level of integration.The computer program product may include a computer readable storagemedium (or media) having computer readable program instructions thereonfor causing a processor to carry out aspects of the present invention.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, configuration data for integrated circuitry, oreither source code or object code written in any combination of one ormore programming languages, including an object oriented programminglanguage such as Smalltalk, C++, or the like, and procedural programminglanguages, such as the “C” programming language or similar programminglanguages. The computer readable program instructions may executeentirely on the user's computer, partly on the user's computer, as astand-alone software package, partly on the user's computer and partlyon a remote computer or entirely on the remote computer or server. Inthe latter scenario, the remote computer may be connected to the user'scomputer through any type of network, including a local area network(LAN) or a wide area network (WAN), or the connection may be made to anexternal computer (for example, through the Internet using an InternetService Provider). In some embodiments, electronic circuitry including,for example, programmable logic circuitry, field-programmable gatearrays (FPGA), or programmable logic arrays (PLA) may execute thecomputer readable program instructions by utilizing state information ofthe computer readable program instructions to personalize the electroniccircuitry, in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce acomputer-implemented process, such that the instructions which executeon the computer, other programmable apparatus, or other device implementthe functions/acts specified in the flowchart and/or block diagram blockor blocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the blocks may occur out of theorder noted in the Figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of onemore other features, integers, steps, operations, element components,and/or groups thereof.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

What is claimed is:
 1. A computer program product for data compression,the computer program product comprising a computer readable storagemedium having program instructions embodied therewith, the programinstructions being readable and executable by a processing circuit tocause the processing circuit to: execute software compression for firstrequests for data compression that have respective sizes below apredefined threshold at the processing circuit; forward second requestsfor data compression having respective sizes above the predefinedthreshold to a hardware accelerator, which is configured to perform datacompression faster than the processing circuit, and which is remote fromthe processing circuit whereby forwards of the second requests to thehardware accelerator are associated with time and processing costs thatare amortizable by the predefined threshold being relatively large ascompared to the respective sizes of the first requests; maintain apersistence of a compression dictionary used for executing the secondrequests across executions of the first and second requests, whereinmaintenance of compression dictionary persistence comprises: padding acompression dictionary with padding space in accordance with a size of afirst request; adjusting a compression dictionary starting location bythe size of the first request and keeping a running total of compressiondictionary starting location adjustments each time a subsequent firstrequest is executed and the compression dictionary is padded, and theprogram instructions further cause the processing circuit to inform thehardware accelerator of an offset in accordance with the running totalof the compression dictionary starting location adjustments; and executesoftware compression for the second requests for data compression at thehardware accelerator with the offset.
 2. The computer program productaccording to claim 1, wherein an execution of software compression forone or more of the first requests comprises one of: compressionperformance with a limited look-back context; and a repackaging ofrequest data into a copy block.
 3. The computer program productaccording to claim 2, further comprising a tracking and manipulation ofrepackaged data.
 4. The computer program product according to claim 1,wherein the program instructions further cause the processing circuit tore-prime the compression dictionary for a next second request.
 5. Acomputer system for data compression, the computer system comprising acomputer readable storage medium having instructions stored thereon thatare executable by a processing circuit to cause the processing circuitto: execute software compression for first requests for data compressionthat have respective sizes below a predefined threshold at theprocessing circuit; forward second requests for data compression havingrespective sizes above the predefined threshold to a hardwareaccelerator, which is configured to perform data compression faster thanthe processing circuit, and which is remote from the processing circuitwhereby forwards of the second requests to the hardware accelerator areassociated with time and processing costs that are amortizable by thepredefined threshold being relatively large as compared to therespective sizes of the first requests; and maintain a persistence of acompression dictionary used for executing the second requests acrossexecutions of the first and second requests, wherein maintenance ofcompression dictionary persistence comprises: padding a compressiondictionary with padding space in accordance with a size of a firstrequest; adjusting a compression dictionary starting location by thesize of the first request and keeping a running total of compressiondictionary starting location adjustments each time a subsequent firstrequest is executed and the compression dictionary is padded, and theprogram instructions further cause: the processing circuit to inform thehardware accelerator of an offset in accordance with the running totalof the compression dictionary starting location adjustments; and thehardware accelerator to execute software compression for the secondrequests for data compression with the offset.
 6. The computer systemaccording to claim 5, wherein the hardware accelerator is embodied in acard element, which is removable from the computer system.
 7. Thecomputer system according to claim 5, wherein an execution of softwarecompression for one or more of the first requests comprises one of:compression performance with a limited look-back context; and arepackaging of request data into a copy block.
 8. The computer systemaccording to claim 7, further a tracking and manipulation of repackageddata.
 9. The computer system according to claim 5, wherein theinstructions further cause the processing circuit to re-prime thecompression dictionary for a next second request.